Phil Plait has a good writeup on some recent space news. He writes that the Murchison meteorite:
…which fell on Australia in 1969, has been found to contain purines and pyrimidines, which are crucial to a large number of biological molecules like DNA, RNA, and ATP….
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Now the good part: scientists studying the Murchison meteorite have determined that the purines and pyrimidines — specifically, uracil and xanthine — have a non-terrestrial origin. In other words, the molecules in this meteorite, so crucial for life, were actually formed in outer space and fell to Earth.
Fundies like to yelp a lot that evolution doesn’t explain the origin of life. That’s right. We never claimed it did. The next time I hear that from a fundie, I’m going to reply “And Jesus didn’t invent popcorn!” That’s just as nonsensical of a statement.
The origin of life on Earth is an awfully good question, but we haven’t exactly figured out how it happened. Somehow, we had to go from the simple molecules that existed on the early Earth—such as carbon dioxide, methane, ammonia, etc.—and get to the more complex molecules that are part of living systems.
Some scientists think that environmental conditions on Earth were sufficient to turn the simple inorganic molecules into complex organic molecules. The most famous experiment to test this hypothesis was the Miller-Urey experiment. That experiment did change the inorganic starting material into organic compounds, including amino acids. You can read about the arguments for and against those results elsewhere, but similar experiments with different conditions have been run in the decades since. In many of these experiments, organic compounds were produced. These results indicate that the formation of organic molecules in the early days of Earth is a realistic and plausible hypothesis.
Another hypothesis is that the complex organic molecules formed elsewhere in the universe and rained down upon the Earth in a hail of meteors, asteroids, and comets. This idea is known as panspermia. The discovery of organic molecules in the Murchison meteorite shows that the panspermia hypothesis is also plausible.
It’s important to realize that this discovery does not prove panspermia. All it shows is that organic molecules can form elsewhere. So now we have two good hypotheses about the origin of life.
